The field of the present invention is timing mechanisms for the exhaust ports of two cycle engines.
Two-cycle engines typically employ the upper edge of a piston as the means for timing the opening and closing of exhaust ports. In such engines, the exhaust passage may be tuned such that a reflected wave of pressure initiated by the opening of the exhaust ports can force unburned air fuel mixture, trailing the exhaust gases through the exhaust passage, back into the cylinder just prior to closure of the exhaust porting This tuning is specifically effective at a limited range of engine speeds. Often power can drop off remarkably when the engine speed does not fall within the tuned range.
To broaden the effective power range for two-cycle engines, exhaust timing control devices have been employed which provide an apparent upper timing edge to the exhaust porting that may be moved upwardly or downwardly depending on engine speed. In this way, power can be realized across a broader range of engine speeds. As the timing for both the opening and closing of the exhaust porting is changed through movement of a valve mechanism, the timing can better employ the pressure wave in the exhaust passage.
A difficulty which has been encountered with such timing mechanisms located within the exhaust passages of a two-cycle engine is that carbon can build up and prevent the proper actuation of the timing device. This can eventually result in a totally inoperative condition.